Public education is a pivotal institution in the United States because it helps children reach their full potential and progress toward a healthy and productive adult life. In that context, successful adaptation to middle school paves the way for higher educational attainment and long-term positive development. Higher levels of education are indeed related to gainful employment, good health, and positive community involvement in adulthood. Peers play a major role in young adolescents' life, and understanding the mechanisms through which they may influence academic adjustment is crucial to refining our theoretical models and developing efficient interventions to promote higher graduation rates. To better understand the contribution of peers to adolescents' adjustment, we propose 4 specific aims: (1) Test for the peer socialization hypothesis. We will investigate the position of group-level and dyadic peer experiences in the mediation chain leading to academic adjustment in middle school. We will verify whether friendships with well-adjusted peers mediate the link between peer acceptance and academic adjustment, and whether friendships with deviant peers mediate the link between peer rejection and academic adjustment. (2) Test for the norm transmission hypothesis. We will test a mediation model in which adolescents with well-adjusted friends internalize prosocial norms, which in turn leads to higher academic adjustment. We will also test for another model in which adolescents with deviant friends internalize antisocial norms, which leads to lower academic adjustment. (3) Test for the niche searching hypothesis. We will verify whether peer rejection leads to lower academic adjustment through academic disengagement, and whether peer acceptance leads to higher academic adjustment through greater academic involvement. (4) Test for the influence of peer socialization on adult educational attainment. We will test whether peer experiences in middle school predict early adult educational attainment through their positive or negative influence on academic adjustment in high school. We will conduct a secondary analysis of existing data from two samples of participants recruited at middle school entry (age 12 years). The first sample includes 997 participants (53% males) from a multiethnic, urban area of the Pacific Northwest, who were followed until age 23. The second sample includes 1,278 participants (46% males) recruited in a predominantly European American suburban area of the Pacific Northwest, who were followed until age 14. Peer acceptance and rejection, friends' characteristics, academic adjustment, and control variables were assessed through self- reports, teacher reports, peer nominations, and official school records. Mediation chains will be tested using structural equation modeling. The moderating effect of gender will also be assessed. Long-term objectives of this project include the improvement of clinical services and screening procedures for at-risk students in middle schools and a redesign of educational environments to optimize positive peer influences and to prevent harmful effects of deviancy training or peer rejection. PUBLIC HEALTH RELEVANCE: Public health in the United States can be enhanced by promoting higher levels of educational attainment, a reliable predictor of health, productivity, employment, and community involvement. Students' perseverance during the high school years and beyond depends on their academic adjustment as early as middle school-a time of their life when peer relationships are particularly significant. It is necessary to understand the mediation chains explaining the association between peer experiences and academic adjustment in middle school to redesign school environments in a way that will enhance adolescents' social and academic success in this setting.